The RPC addresses the challenges facing investigators who conduct behavioral and biobehavioral research on special populations (e.g., individuals with autism, FXS, DS). Such populations are difficult to recruit, require diagnostic evaluations by professionals with specialized training, and often need to be assessed via innovative measurement strategies designed to focus specifically on the construct of interest. The RPC helps IDDRC investigators deal with these and other challenges in the areas of recruitment, assessment, and behavioral methods development and applications. Although the RPC received a rating of outstanding in the previous competitive review of the IDRRC, the Core has changed significantly in the past five years in the following ways. The RPC has created local and national partnerships to ensure more cost-effective recruitment of special populations; changed its recruitment strategies to adapt to changing demographics and the new ways in which people communicate; added cutting-edge technology and expertise to support it; and devoted more resources to supporting biobehavioral and translational research, while maintaining its long-standing commitment to behavioral science. Leadership of the RPC changed in 2010 when former Core Director Len Abbeduto accepted the position of Director of the MIND Institute at UC-Davis. The name of the Core reflects our goal of supporting the participation of human subjects in research, including recruitment, the provision of clinical expertise for behavioral assessments, and support of technology for enhancing characterization efforts.